The invention pertains to a device for the slicking, stretching and drying of leather or similar flat materials such as hides, skins and the like.
It is known from DE 30.10.003 how pieces of leather, pressed together by a vacuum in the interstice between two elastically extensible foils, can be stretched by extending these foils simultaneously.
A device, representing the next state of the art, is known from DE 38.33.068, in which pieces of leather are stretched in the interstice between a low friction support surface and an elastically extensible membrane under vacuum. As opposed to the device according to DE 30.10.003, the employment of a rigid support surface of material with high thermal conductivity permits use as a combined stretching and drying machine, the moisture evaporating from the leather being drained through a relief structure on the membrane, which is connected with a suction device.
The primary disadvantage of this device is that, in spite of the low friction support surface, the contact pressure forces on the leather act against the stretching force. The resistance (friction) thus caused prevents optimum pick-up of the leather and uniform stretching of its whole area, limiting the dimensional increase which can be achieved. In the process, there is great strain on the elastic membrane. Its resulting limited service life leads to increased running costs for the machine. Furthermore, this device is only suitable for the treatment of skins with a low water content (approx. 25%) and is unsuitable for very wet leather.
From the French patent application 2602795, a device is known which conforms with the general concept of the invention.
This shows triangular lamellae which can be radially extended outwards from their closed position as shown in FIG. 1 to the position shown in FIG. 3, thus stretching the hide. The essential, differentiating characteristic of the device according to this patent application is that the lamellae swing outwards around a fixed point as in an iris aperture. As a result of this special movement of the lamellae, no spaces occur between the lamellae during the movement, but a central widening opening is formed, so that the already stretched sections of the hide in this area can already be pressed flat and dried. Furthermore, because of the special form of the lamellae, the stretched hide is held fast over its entire circumference at the limit position of the lamellae.
In contrast to this, in accordance with the French patent application, as the lamellae move outwards, spaces occur between them in which the hide is no longer held. When the triangular lamellae are deployed outwards, the hide is only held by the tips of the lamellae, thus with a relatively small surface area, while large parts of the circumference of the hide are no longer held by the lamellae.
Vacuum drier units are also known which can also dry very wet leather. The slicking out of surplus water here is carried out manually. However, here the leather is only dried, not simultaneously stretched; in fact, it actually shrinks.
The function of the invention is the creation of a device which eliminates the high friction forces during stretching of the leather under vacuum, in that the leather support surface is formed of elements which carry with them the whole surface of the leather and the contact pressure device without friction resistance to the support surface, resulting in optimum area enlargement, and is also able to stretch and dry very wet leather simultaneoulsy and, if necessary, to slick it out first.
The problem is solved in accordance with this invention in that, over a smooth, low friction, support surface, consisting of thermally conductive material and heated by hot water, oil or another medium, movable lamellae are fitted, which are connected with a drive mechanism to deploy them in a circle outwards from the centre around a fixed point. These lamellae form the actual stretching mechanism, while the primary function of the stacked contact pressure device, consisting of a sheet of extensible material with channels, nubs, perforations and the like for drainage of the moisture from the leather, is fixation. The contact pressure device may also consist of a rigid, inextensible plate, the surface of which is provided with channels, perforations and the like for drainage of moisture from the leather. On this, a second mirror-image lamella system is mounted, so that the leather is stretched between the two outwards deployable lamella systems and is fixed by the rigid contact pressure plate.
In the following, versions of the device constituting the invention are explained with the help of drawings.